The extensive data storage needs of modern computer systems require large capacity mass data storage devices. A common storage device is the rotating magnetic disk drive.
A disk drive typically contains one or more smooth, flat disks which are rigidly attached to a common hub or spindle. The disks are stacked on the spindle parallel to each other and spaced apart so that they do not touch. A clamping mechanism rigidly secures the disk or disks to the hub. The disks and hub are rotated in unison at a constant speed by a spindle motor.
Each disk is formed of a solid disk-shaped base or substrate, having a hole in the middle for the spindle. The substrate is commonly aluminum, although glass, ceramic, plastic or other materials are possible. The substrate is coated with a thin layer of magnetizable material, and may additionally be coated with a protective layer.
Data is recorded on the surfaces of the disks in the magnetizable layer. To do this, minute magnetized patterns representing the data are formed in the magnetizable layer. The data patterns are usually arranged in circular concentric tracks. Each track is further divided into a number of sectors. Each sector thus forms an arc, all the sectors of a track completing a circle.
A moveable actuator positions a transducer head adjacent the data on the surface to read or write data. The actuator may be likened to the tone arm of a phonograph player, and the head to the playing needle.
There is one transducer head for each disk surface containing data. The transducer head is an aerodynamically shaped block of material (usually ceramic) on which is mounted a magnetic read/write transducer. The block, or slider, flies above the surface of the disk at an extremely small distance as the disk rotates. The close proximity to the disk surface is critical in enabling the transducer to read from or write to the data patterns in the magnetizable layer. Several different transducer designs are used, and in some cases the read transducer is separate from the write transducer.
The actuator usually pivots about an axis to position the head. It typically includes a solid block near the axis having comb-like arms extending toward the disk, a set of thin suspensions attached to the arms, and an electro-magnetic motor on the opposite side of the axis. The transducer heads are attached to the suspensions, one head for each suspension. The actuator motor rotates the actuator to position the head over a desired data track. Once the head is positioned over the track, the constant rotation of the disk will eventually bring the desired sector adjacent the head, and the data can then be read or written.
The clamp that secures one or more data storage disks within an enclosure for rotation in unison with a hub must meet several well recognized design constraints. Among these are the ability to preclude slippage of the disk relative to other portions of the rotating assembly during acceleration and deceleration of the spindle assembly and the capability to resist side shock loads without displacement of a disk with respect to the balance of the assembly. In addition, the clamping force must not distort the disk and the clamp must be capable of assembly and removal without damage to other assembly components including the disks, spindle motor or spindle bearing assemblies and further, the device must not be the source of contaminants within the enclosure in the form of either debris or outgassing of the component materials.
A typical clamping technique is the use of a series of screws that are equiangularly spaced to secure a circular clamp to compressively retain the disk or disks between the clamp and a flange formed as a part of the hub. This technique results in the localized distortion of the disk adjacent the site of each screw. This phenomena was of little consequence when larger disk sizes and lower a real recording densities were used, but such factors are of concern as disk drive miniaturization occurs. Further, with drives using 1.8 inch diameter disks and subject to the dimensional limitations of the associated form factor, the use of a pattern of clamping bolts with the required torque limitations is an unacceptable solution for purposes of mass production manufacturing.
A solution which is a more acceptable manufacturing technique is the use of a shrink fit clamp which is assembled using the required clamping force and allowed to cool and establish a shrink fit about the hub. However, when this approach is utilized in the environment of a small drive using a 1.8 inch diameter disk, the radial constricting forces tend to affect the running accuracy of the bearing assembly that is mounted at the opposite side of the same hub wall.
Any clamping technique must be considered with respect to the problems of radial and axial runout that can be influenced by distortion induced by the clamping forces. Radial distortion causes tracks to become non-circular, but the problem can be overcome by writing the tracks subsequent to assembly of the disks to the hub. Axial runout is the variation in disk flatness or the departure from a planar surface that tend to vary the flyheight of the transducer head during a cycle of rotation. As the air bearing separating the transducer head from the disk becomes smaller, such as approaching two microinches, the disk flatness becomes a significant concern and phenomena, such as disk clamping, that influence such flatness must not impair or compromise this disk parameter.
The objective is to design an inexpensive clamp with an extra low profile to provide both axial and radial clamping forces. Although many of the design problems have long been recognized, the attendant difficulties have become progressively more acute as requirements call for continuously higher areal data recording densities and smaller physical dimensions. Disk diameters of the smallest disk drives have progressed from 3.5 inches, to 2.5 inches, and presently to 1.8 inches. In addition, it must be anticipated that the future will have a requirement for a drive using one inch diameter disks.